Two-stroke diesel engine with an exhaust gas driven turboblower



July 2, 1963 I G. WOLF I 3,095,692

TWO-STROKE DIESEL ENGINE WITH AN EXHAUST GAS DRIVEN TURBOBLOWER FiledJune 26, 1961 2 Sheets-Sheet 1 Jnvenfar:

GOTTL/EB VVOLE July 2, 1963 G. WOLF 3,095,692 TWO-STROKE DIESEL ENGINEWITH AN EXHAUST GAS DRIVEN TURBOBLOWER Filed June 26, 1961 2Sheets-Sheet 2 Fig.3

Jnvenfor: GorruEBVVLF. 13 /K United States Patent F r 3,095,692TWO-STROKE DIESEL ENGINE WITH AN EX- HAUST GAS DRIVEN TURBOBLDWER'Gottlieb Wolf, Winterthur, Switzerland, assignor to Sulzer Freres, S.A.,Wintcrthur, Switzerland, a corporation of Switzerland Filed June 26,1961, Ser. No. 119,611 Claims priority, application Switzerland July 11,1960 1 Claim. (Cl. 6013) The invention relates to a two-stroke dieselengine with an exhaust gas turboblower and adjustable preexhaust bymeans of at least one cam-operated exhaust control device.

In order to maintain the turbine speed in low load or speed ranges oftwo-stroke diesel'engines having an exhaust gas driven turboblower, itis known to open the exhaust valve prematurely whereby the preexhaustangle, i.e. the angle difference measured at the crankshaft between theopening of the exhaust and the beginning of scavenging, is increased. Inthis way, more power is fed to the turbine at the'expense of the engine.In one known construction this is effected by turning the camshaft whichoperates the exhaust valves, relative to the crankshaft in dependence onthe scavenging air pressure and in a direction to advance opening of theexhaust valves as the air pressure drops. This arrangement has thedisadvantage that earlier opening of the preexhaust valves isaccompanied by their earlier closing and that it is not possible tocorrectly shape the cam for the individual load ranges. Since the camsfor the fuel injection arenormally disposed on the same camshaft as thecams for :the exhaust valves the cams for the fuel injection and thecams of the exhaust valves are simultaneously adjusted in a manner whichis not desired. It has also been proposed to construct the exhaust valvecontrol cam as a function body which is axially slidable in dependenceon the scavenging pressure so that the cam tracks pertaining to theindividual scavenging pressures can be properly constructed. With thepower and space conditions prevailing in diesel engines, however, thepoint contact between the cams and the cam follower rollers inherent inthe aforesaid mechanism makes it impossible to construct and accommodatecams which give satisfactory service.

'It is an object of the invention to provide an exhaust control devicewhich combines the advantages of known devices and avoids theirdisadvantages and whichincludes an axially slidable cam having for atleast one direction of rotation of the engine cylindrical control tracksfor I not more than three and at least two different ranges ofoperation, the change-over of the exhaust control device from one oftheindividual tracks to another being effected stepwise when thepredetermined ranges of operation are exceeded.

The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, and additional objects and advantages thereof will bestbe understood from the following description of an embodiment thereofwhen read in connection with the accompanying drawing wherein:

FIG. 1 is a diagrammatic illustration of a diesel engine with an exhaustgas driven turbosupercharger and preexhanst control according to theinvention.

FIG. 2 is an enlarged view of a cam forming part of the control shown inFIG. 1, looking in the direction of the arrow B of FIG. 1.

FIG. 3 is. a diagram illustrating the principle of the invention.

Referring more particularly to FIG. 1, scavenging ports 6 are providedin a cylinder 1 of a reversible two-stroke marine engine including apiston 2, a piston rod 3, a crankshaft 4 and a crankcase 5. Thescavenging ports 6 3,095,692 Patented July 2, 1963 are connected to anair supply socket 7 connected to an outlet 8 of a compressor 9. Thelatter is provided with an inlet pipe 10. A valve 12 controlling anexhaust pipe 11 is disposed in the cylinder 1 and provided with a valvespring 13. The valve is adapted to be operated by a cam element 1 7through a rocker arm 14, a push rod 15 and a roller 16. An inlet 18 ofan exhaust gas turbine 19 is connected to the exhaust pipe 11. Therotors of the turbine 19 and of the compressor 9 are connected by acommon shaft 20. A camshaft 22 driven by the engine through gears 23,24, 25 is axially slidably and rotatably supported by bearings 26. Forthe sake of clarity, the shaft 22 has been illustrated as being normalto the crankshaft 4. Actually, it is parallel to the crankshaft 4. Theshaft 22 is provided with two collars 27 between which extends an arm ofan angle lever 28. The latter is connected by a rod 29 and a two-armlever 30 to a servomotor 31 for preexhaust control and a servomotor 32.for forward and reverse operation of the engine. The servomotors 31 and32 are provided with supply lines 33, 34 and control slide valves 35, 35for a hydraulic or pneumatic pressure medium. An element 36 providedwithgrooves 37-39 is mounted on the shaft 22. The grooves are adapted tobe engaged by a spring-loaded retaining piston 40. The-slide valve 35'is operated bya speed regulator 41 which is driven by the shaft 22 byway of helical gears 42, 43.

The cam element 17 has cams I, II and III. The cams I and II areintended for the forward operation and the cam III for the reverseoperation of the engine, which is reversible. Between the individualcams transition surfaces are provided in the conventional manneraffording rolling of the roller 16 from one cam onto the other uponaxial displacement of the shaft 22. The cam surfaces are formed by axialgenerating lines .and have a noncircular cross section.

When the engine operates in forward direction and at low speeds theroller 16 is on the cam I of the cam element 17. Upon exceeding apredetermined engine speed the control slide valve 35 is moved to theright, as seen in FIG. 1, by means of the regulator 41 so that thepiston of the servomotor 31-is moved into its bottom position, causinganticlockwise swinging of the angle lever 28. The angle lever 28 pushesthe shaft 22 to the right and the roller 16 begins to roll on the cam IIwhich is intended for a higher engine speed and which effects a smallerpreexhaust angle. Q

If reverse operation of the engine is desired the shaft 22 is moved to:the left by means of the regulator M ami the servornotor 31 after acorresponding reduction of the speed until the roller 16 again'comes tomove on the cam I of the cam element 17 Ont-he subsequently initiatedreverse starting maneuver the piston of the control slide valve 35 ismoved to the right and the piston of the servomotor 32 passes into itstop position. The shaft 22 is thereby moved to the left by way of theangle lever 28 until the roller 16 moves on the cam III of the camelement 17, making the engine ready for reverse operation.

FIG. 2 is a view of the cam element 17 in the direction of the arrow Bin'FIG. 1. FIG. 2 shows that the cam I has a lo'be causing an earlierbeginning of opening a of the exhaust valve than the cam II which causesopening of the exhaust valve at the angular position b of the shaft 22.The cam I causes-full opening of the valve 1 2 at the position c whereasthe cam II causes full opening at the position d. Closing of the exhaustvalve begins with these cams at the same time at the position e for bothspeeds and terminates at the position 1 for both speeds. The cam IIIprovided for reverse travel is symmetrical with the cam I and is shownby a broken line. If the same maximum speed is required for reverseoperation as for forward operation, a cam IV is provided 3 which issymmetrical to the cam II and which is shown by a dash-dot line.

In FIG. 3 the curve a shows the optimal preexhaust angle V, for example,with respect to fuel consumption and smoke at steady operatingconditions, in dependence on the speed n in the case of a marine enginewith direct drive of the propeller. Tests have shown that the curve a ishorizontal between 40% and full load speed, i.e., for this range asingle adjustment of the preexhaust angle is sufficient. Below 40% ofthe full load speed it is necessary to increase the preexhaust angle, asshown by the inclined curve portion a. According to the invention, forthe range from about 40% of full load speed up to maximum speed thepreexhaust angle adjustment used is the one obtained by the cam II ofthe cam element 17. Below this speed range the cam I comes intooperation, which produces an increased preexhaust angle. The diagramshows that the actually eifected preexhaust angle considerably exceeds(the theoretically required preexhaust angle. This means that theturbosupercharger group receives more energy than required for staticconditions as regards fuel consumption and so on. On the other hand,however, an increased air pressure is obtained for scavenging andcharging and the acceleration power of the engine is considerablyboosted. The result of this is that while in the higher speed range whenthe cam II is in operation an optimum engine economy is obtained, in thelower speed range when the cam I is in operation improved accelerationis obtained, which is particularly important for this speed range. Thisadvantage is particularly striking in the case of marine enginesdirectly driving the propeller. With these engines the power isdependent on the speed in accordance with the known propellercharacteristic, 40% of full load speed corresponding approximately .to6% power. This means that such an engine can be designed for optimumeconomy in practically the entire power range but receives its maximumacceleration in the range below 40% speed and 6% power, i.e., in theidling range. A somewhat increased specific fuel consumption can betolerated in the lower speed range since the total fuel consumption issmall in the low power range. In addition there is the important factthat with such engines a reversing mechanism is always provided and thesystem according to the invention requires only slight changes of thecam and of the reversing mechanism. The engine can be used withoutadditional scavenging pumps or blowers.

Although an engine having two cams for forward direction of rotation hasbeen described as an example, it is possible to provide three cams, i.e.three ranges of operation for special purposes, for example forlocomotive engines and the like.

The paraxial surfaces of the cams permit line contact between the camand the roller, causing only moderate stresses at the lines of contactin comparison with point contact and extending the life of the cams andof the roller.

4 The transition surfaces permit simple displacement of the cams duringthe change-over movement whereby the roller can roll from one cam toanother. A cam construction without transition surfaces is possible,necessitating, however, a device to lift the roller during thechange-over, as is known in devices for changing from forward andreverse operation and vice versa.

The control of the forward operation, reverse operation and preexhaustmay also be effected by apparatus different from that illustrated, forexample, by a displacer servomotor mounted on the camshaft. The speedregulator may also be replaced by a speed responsive hydraulic orpneumatic system.

Furthermore, the adjustment of the cam need not be effected independence on engine operating ranges determined by the speed. Thisadjustment may be effected in dependence on other operating variables ofthe engine, for example the scavenging pressure. In that case, theregulator 41 would be formed by a pressure-sensitive element known perse, which is connected to the scavenging air line.

I claim:

In a reversible two-stroke diesel engine operating under variable loadand having an exhaust gas driven turbocharger, an exhaust valve forcontrolling flow of exhaust gas to said turbocharger, and control meansfor said exhaust valve, said control means including an axially movableshaft rotating at a speed corresponding to the engine speed: a cammounted on said shaft and having three cam surfaces, cam follower meansoperatively connected to said valve and engaged by one of said camsurfaces for operating the engine in one direction of rotation andengaged by the second or third cam surface, depending on the axialposition of said shaft for operating the engine in the oppositedirection of rotation, means responsive to the speed of the engine andconnected to said shaft for axial movement thereof to eifec-t engagementof said second cam surface by said cam follower means upon an enginespeed below a predetermined value and to effect engagement of said thirdcam surfiace by said cam follower means upon an engine speed above saidpredetermined value, to stepwisely advance beginning of the opening ofsaid exhaust valve upon a reduction of the engine speed below saidpredetermined value and to retard beginning of the opening of saidexhaust valve upon increase of the engine speed above said predeterminedvalue.

References Cited in the file of this patent UNITED STATES PATENTS1,159,692 McKeen Nov. 9, 1915 1,161,464 Enrico Nov. 23, 1915 2,097,883Johansson Nov. 2, 1937 2,670,594 Crooks Mar. 2, 1954 2,977,943Lieberherr Apr. 4, 1961 2,991,616 Miller July 11, 1961

